The present invention relates to an image processing system as defined in the preamble of claim 1 and to an image processing procedure as defined in the preamble of claim 5 for the processing of images via a data communication network.
Conventional colour printing is partly an artistic activity. It takes a professional image processing specialist and complicated operations to produce guaranteed image quality. Offset printers are artists in their own field; the inking must be controlled specifically for each image. Digital colour printers have changed the situation. People without any deep knowledge of printing can manipulate, process and print different types of colour images. The digital printing mode enables decentralisation of the various processing operations comprised in printing. Decentralised printing involves new aspects in the production of paper-based reading material. The various stages of production are more individual. An image can be printed with different printers using different printing parameters.
Colour control in printing is traditionally based on colour correction. Colour correction means compensating for the distortion in printing that arises from non-ideal absorption of the spectral coverage of colour in the printing toner. At present, colour correction is based on data obtained via test printing, i.e. there is no reliable computational method available.
In digital image processing, in decentralised printing and in digital colour printers, general colour correction is needed. The term xe2x80x98hardware independent colourxe2x80x99 simply means that the values of digitised colour code and a system of chromaticity coordinates for the printer are defined by convention. These relationships have been modified by balancing the visual system of chromaticity coordinates, such as CIELab and CIELuv. As regards hardware independence, the system of chromaticity coordinates can also be defined in terms of RGB or CMYK. The idea of hardware independence has been extended to decentralised printing systems in a data communication network environment, by defining profiles separately for each input device and each output device. When different devices are connected to the system, the same hardware levels and uniform control methods are used. The profiles are colour correction descriptors for different correction operations, which have to be defined experimentally. This means that the profiles for all possible inputs and outputs must be known. This naturally restricts the concept of decentralised printing as an independent system regarding place and time.
The old idea about the printing of a colour image is that the oraginal image is a model for the printing. This is a misleading idea because the true colours of the original image are not necessarily known. The image may have been digitised with a cheap camera or the image has been generated by an older coding method, which may result in inadequate image quality. If the image is to be printed, it has to be enhanced and corrected.
The object of the present invention is to eliminate the drawbacks mentioned above.
The image processing system comprises four different types of device; an input device, an image enhancing device, a display terminal and an output device. All devices are independently connected to a data communication network. Each device knows its own parameters, e.g. the colour correction profile. Each device has artificial intelligence to enable the device to process the data of a source independent image. What was said above means that it is not necessary to know the technical origin of the image. The image can be encoded by any coding method generally used. When the image is processed by a device comprised in the image processing system in question, a signal section can be added to the image code. The signal section may contain e.g. illumination information about the object of the image and make-up information about image processing.
When the system of the invention is compared with conventional colour printing, one new requirement regarding changed working principles emerges. Today, those who use colour printing are editors, writers and computer users in general, whereas ten years ago they were professional image operators. Interactive image make-up operations are optional, but not indispensable for an acceptable printing result.
As for the features characteristic of the invention, reference is made to the claims.
The image processing system of the invention comprises a data communication network, which serves as a channel for the transmission of the image being processed, digitised in an electronic form of representation, and which connects an image processing device comprised in the system. The image processing device processes the image and prints it to different formats. According to the invention, the image processing device comprises an image enhancing device. The image enhancing device automatically classifies and corrects the image. The image enhancing device may also only classify or only correct the image.
In the procedure of the invention, an image digitised in an electronic form of representation is transmitted in a data communication network, in which the image is processed by means of different devices. The processing is aimed at improving the visual quality of the image. Besides improving the visual quality of the image, the image is printed to different formats; in other words, the image can be printed e.g. to a display terminal or on paper. According to the invention, the image is automatically classified on the basis of a signal section comprised in the image code, and, based on the classification, corrections are made in the image.
The image processing system is decentralised so that the system input, a separate image processing device, a display terminal and the system output can be disposed in different locations and the functions of different devices can be performed at different times. Each device in the system only needs the image code. No technical parameters of the other devices are needed. Such a system can be said to be source and device independent.
In an embodiment of the device, the image processing system comprises a profile generating device, in which the image is processed on the basis of device-specific properties.
In an embodiment of the device, the image processing system comprises an adding device arranged to add information code to the image, which information code may contain e.g. information about the illumination conditions of the image, image correction operations and image quality in general.
In an embodiment of the device, the image is in digital format in the image processing system. The digital image format may have been encoded by many different methods commonly used.
According to an embodiment of the procedure, in the automatic image correction, edge areas in the image are first identified. Next, gamma correction of the image is carried out. After this, the grey shade balance, brightness and RGB contrast of the image are adjusted. Finally, the sharpness of the image is enhanced, image noise is filtered and the colour memory is adjusted.
In an embodiment of the procedure, the image is processed in the output device in accordance with the profile, i.e. characteristic features of the output device.
In an embodiment of the procedure, the automatic image correction function uses information obtained from a standard observer. The observer is shown different images, of which he/she selects a preferred image, based on certain criteria.
In an embodiment of the procedure, output device-specific correction is carried out after automatic classification and correction.